U.S. patent application number 15/042610 was filed with the patent office on 2016-09-08 for lighting device, head light and vehicle.
The applicant listed for this patent is Panasonic Intellectual Property Management Co., Ltd.. Invention is credited to Takahiro FUKUI, Kazutoshi SUGANUMA, Toshifumi TANAKA.
Application Number | 20160262232 15/042610 |
Document ID | / |
Family ID | 56738578 |
Filed Date | 2016-09-08 |
United States Patent
Application |
20160262232 |
Kind Code |
A1 |
FUKUI; Takahiro ; et
al. |
September 8, 2016 |
LIGHTING DEVICE, HEAD LIGHT AND VEHICLE
Abstract
A lighting device includes first to third output terminals, a
power converter, a bypass switch, and a controller. A first light
source is connected between the first and third output terminals. A
second light source is connected between the second and third
output terminals. The bypass switch is connected between the second
and third output terminals. The controller switches the bypass
switch between ON-state and OFF-state. The controller controls the
power converter to adjust an output current. The controller
includes a voltage meter for measuring a voltage corresponding to
an output voltage of the power converter. The controller compares a
measured voltage of the voltage meter with a first threshold
voltage while keeping the bypass switch in OFF-state. The
controller compares the measured voltage with a second threshold
voltage while keeping the bypass switch in ON-state. The second
threshold voltage is smaller than the first threshold voltage.
Inventors: |
FUKUI; Takahiro; (Osaka,
JP) ; TANAKA; Toshifumi; (Osaka, JP) ;
SUGANUMA; Kazutoshi; (Niigata, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Intellectual Property Management Co., Ltd. |
Osaka |
|
JP |
|
|
Family ID: |
56738578 |
Appl. No.: |
15/042610 |
Filed: |
February 12, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05B 45/00 20200101;
H05B 45/37 20200101; B60Q 11/00 20130101; H05B 45/44 20200101; B60Q
1/04 20130101 |
International
Class: |
H05B 33/08 20060101
H05B033/08; B60Q 1/04 20060101 B60Q001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 2015 |
JP |
2015-040541 |
Claims
1. A lighting device for lighting a DC light source including a
first light source and a second light source, the lighting device
comprising: a first output terminal to be electrically connected to
a first end of the first light source; a third output terminal to
be electrically connected to a second end of the first light source
and a first end of the second light source; a second output
terminal to be electrically connected to a second end of the second
light source; a power converter that includes a DC-DC converter and
a pair of output ends electrically connected respectively to the
first and second output terminals, and is configured to supply an
output current from the DC-DC converter through the pair of output
ends; a bypass switch electrically connected between the second and
third output terminals; and a controller configured to switch the
bypass switch between an ON-state and an OFF-state, and to control
the power converter to adjust the output current of the power
converter, the controller including a voltage meter configured to
measure a voltage corresponding to an output voltage of the power
converter to output a measured voltage, the controller being
configured to while keeping the bypass switch in the OFF-state,
compare the measured voltage of the voltage meter with a
predetermined first threshold voltage, and stop operation of the
power converter when determining that the measured voltage is equal
to or greater than the first threshold voltage, and while keeping
the bypass switch in the ON-state, compare the measured voltage of
the voltage meter with a predetermined second threshold voltage,
and stop the operation of the power converter when determining that
the measured voltage is equal to or greater than the second
threshold voltage, the second threshold voltage being smaller than
a first rated voltage but larger than a second rated voltage, the
first rated voltage corresponding to a rated value of the output
voltage of the power converter under a condition where the bypass
switch is kept in the OFF-state, the second rated voltage
corresponding to a rated value of the output voltage of the power
converter under a condition where the bypass switch is kept in the
ON-state, and the first threshold voltage being larger than the
first rated voltage.
2. The lighting device of claim 1, wherein: the controller is
configured to stop the operation of the power converter when
determining that a state where the measured voltage of the voltage
meter is equal to or greater than a predetermined third threshold
voltage continues for a predetermined first upper limit time while
keeping the bypass switch in the OFF-state; and the third threshold
voltage is larger than the first rated voltage but smaller than the
first threshold voltage.
3. The lighting device of claim 1, wherein: the controller is
configured to stop the operation of the power converter when
determining that a state where the measured voltage of the voltage
meter is equal to or greater than a predetermined fourth threshold
voltage continues for a predetermined second upper limit time while
keeping the bypass switch in the ON-state; and the fourth threshold
voltage is larger than the second rated voltage but smaller than
the second threshold voltage.
4. The lighting device of claim 1, wherein: the controller is
configured to, during a predetermined wait time period after
switching the bypass switch from the OFF-state to the ON-state or
after switching the bypass switch from the ON-state to the
OFF-state, compare the measured voltage of the voltage meter with
the first threshold voltage, and stop the operation of the power
converter when determining that the measured voltage is equal to or
greater than the first threshold voltage.
5. The lighting device of claim 1, wherein: the bypass switch
includes a transistor; and the controller is configured to increase
current flowing thorough the bypass switch with an increase in
elapsed time in a process of switching the bypass switch from the
ON-state to the OFF-state, and to decrease the current flowing
thorough the bypass switch with an increase in elapsed time in a
process of switching the bypass switch from the ON-state to the
OFF-state, by means of an amplification action of the bypass
switch.
6. The lighting device of claim 1, wherein: the controller is
configured to, during a predetermined time period after switching
the bypass switch between the ON-state and the OFF-state, compare
the measured voltage of the voltage meter with a fifth threshold
voltage, and stop the operation of the power converter when
determining that the measured voltage is equal to or greater than
the fifth threshold voltage; and the fifth threshold voltage is
larger than the second threshold voltage but smaller than the first
threshold voltage.
7. The lighting device of claim 6, wherein: the controller is
configured to linearly change the fifth threshold voltage between
the first threshold voltage and the second threshold voltage with
an increase in elapsed time after switching the bypass switch
between the ON-state and the OFF-state.
8. The lighting device of claim 1, wherein: the first rated voltage
is defined by a sum of a rated voltage of the first light source
and a rated voltage of the second light source; and the second
rated voltage is defined by the rated voltage of the first light
source.
9. The lighting device of claim 1, wherein: the first light source
is constituted by a first series circuit of LEDs and has a first
forward voltage; the second light source is constituted by a second
series circuit of LEDs and has a second forward voltage; the first
rated voltage is defined by a sum of the first forward voltage and
the second forward voltage; and the second rated voltage is defined
by the first forward voltage.
10. The lighting device of claim 1, further comprising a signal
input terminal for receiving a first instruction signal and a
second instruction signal, wherein: the controller is configured to
keep the bypass switch in the OFF-state while the signal input
terminal receives the first instruction signal, and keep the bypass
switch in the ON-state while the signal input terminal receives the
second instruction signal.
11. The lighting device of claim 1, wherein: the DC-DC converter
includes a switching element; the controller further includes a
current meter configured to measure a current supplied from the
power converter to the DC light source, and to output a measured
current; the controller is configured to control a switching
operation of the switching element such that the measured current
of the current meter is equal to a predetermined target value; and
the controller is configured to while keeping the bypass switch in
the OFF-state, stop the operation of the power converter by turning
off the switching element when determining that the measured
voltage is equal to or greater than the first threshold voltage,
and while keeping the bypass switch in the ON-state, stop the
operation of the power converter by turning off the switching
element when determining that the measured voltage is equal to or
greater than the second threshold voltage.
12. The lighting device of claim 11, wherein: the power converter
further includes an inductor for storing therein energy in response
to supply of electric power from an external DC power source while
the switching element is turned on, and a capacitor to be charged
by a regeneration current from the inductor while the switching
element is turned off; the controller is configured to generate a
primary current instruction value based on the measured current of
the current meter and the target value; and the controller is
configured to turn off the switching element when a primary current
flowing through the switching element reaches the primary current
instruction value, and turn on the switching element when the
regeneration current reaches zero or when a predetermined
suspension time elapses from a time when the switching element is
turned on last time.
13. A headlight, comprising: the lighting device of claim 1; a DC
light source to be lit by electric power supplied from the lighting
device; and a housing that houses the DC light source.
14. A vehicle, comprising: the headlight of claim 13; and a vehicle
body in which the headlight is installed.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is based upon and claims the benefit
of priority of Japanese Patent Application No. 2015-040541, filed
on Mar. 2, 2015, the entire contents of which are incorporated
herein by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to a lighting device, a
headlight, and a vehicle.
BACKGROUND ART
[0003] JP2011-233264A discloses a conventional lighting device.
This lighting device is configured to apply a DC (direct-current)
voltage to a load (a light source), which is constituted by a
series circuit of light-emitting diodes (LEDs), to operate (light)
the light source. This lighting device includes a bypass switch to
be connected in parallel to particular ones of the LEDs (some of
the LEDs on a lower potential side). Accordingly, when the bypass
switch is turned off, the lighting device operates (lights) all of
the LEDs. On the other hand, when the bypass switch is turned on,
the bypass switch acts as a short circuit between both ends of the
particular ones of the LEDs, and thus the lighting device operates
(lights) only the rest of the LEDs.
[0004] This conventional lighting device further includes a voltage
measuring circuit for measuring a voltage (an output voltage)
applied across the light source, a current measuring circuit for
measuring a current flowing through the light source, and a failure
detecting portion for determining, based on measuring results of
these measuring circuits, whether failure has occurred. When
determining that the output voltage is out of a predetermined
normal range (10 to 40 V, for example), the failure detecting
portion determines occurrence of failure and stops the operation of
the lighting device. For example, abnormal increase in the output
voltage may be caused by a breakdown of the bypass switch in an
open mode (hereinafter referred to as "open circuit failure").
[0005] Apart from the case of the open circuit failure, the output
voltage possibly increases abnormally due to another reason, such
as a bad connection between connectors of the lighting device and
the light source (the LEDs). It should be noted that in the case of
the bad connection between the connectors, external factors such as
vibration may cause a change in the connection state of the
connectors between a state where the connectors are connected
correctly and a state where the connectors are not connected
correctly. In this regard, therefore, a voltage higher than a
desired voltage may be applied to the light source when the
connection state of the connectors recovers from the incorrectly
connected state to the correctly connected state, and as a result
of which the light source may be damaged or cause a failure.
SUMMARY
[0006] The present disclosure relates to a lighting device capable
of detecting occurrence of an abnormal output voltage and
suppressing occurrence of a failure, and a headlight, and a
vehicle, including the lighting device.
[0007] A lighting device according to an aspect of the present
disclosure is for lighting a DC light source including a first
light source and a second light source. The lighting device
includes: a first output terminal to be electrically connected to a
first end of the first light source; a third output terminal to be
electrically connected to a second end of the first light source
and a first end of the second light source; a second output
terminal to be electrically connected to a second end of the second
light source; a power converter that includes a DC-DC converter and
a pair of output ends electrically connected respectively to the
first and second output terminals, and is configured to supply an
output current from the DC-DC converter through the pair of output
ends; a bypass switch electrically connected between the second and
third output terminals; and a controller configured to switch the
bypass switch between an ON-state and an OFF-state, and to control
the power converter to adjust the output current of the power
converter. The controller includes a voltage meter configured to
measure a voltage corresponding to an output voltage of the power
converter to output a measured voltage. The controller is
configured to, while keeping the bypass switch in the OFF-state,
compare the measured voltage of the voltage meter with a
predetermined first threshold voltage, and stop operation of the
power converter when determining that the measured voltage is equal
to or greater than the first threshold voltage, and while keeping
the bypass switch in the ON-state, compare the measured voltage of
the voltage meter with a predetermined second threshold voltage,
and stop the operation of the power converter when determining that
the measured voltage is equal to or greater than the second
threshold voltage. The second threshold voltage is smaller than a
first rated voltage but larger than a second rated voltage, the
first rated voltage corresponding to a rated value of the output
voltage of the power converter under a condition where the bypass
switch is kept in the OFF-state, the second rated voltage
corresponding to a rated value of the output voltage of the power
converter under a condition where the bypass switch is kept in the
ON-state. The first threshold voltage is larger than the first
rated voltage.
[0008] A headlight according to an aspect of the present disclosure
includes the lighting device, a DC light source to be lit by
electric power supplied from the lighting device, and a housing
that houses the DC light source.
[0009] A vehicle according to an aspect of the present disclosure
includes the headlight and a vehicle body in which the headlight is
installed.
BRIEF DESCRIPTION OF DRAWINGS
[0010] The figures depict one or more implementations in accordance
with the present teaching, by way of example only, not by way of
limitations. In the figures, like reference numerals refer to the
same or similar elements where:
[0011] FIG. 1 is a circuit diagram of a lighting device according
to Embodiment 1;
[0012] FIG. 2 is a flow chart of an operation of the lighting
device;
[0013] FIG. 3 is a time chart of an operation of the lighting
device;
[0014] FIG. 4 is a time chart of an operation of the lighting
device;
[0015] FIG. 5 is a flow chart of an operation of a lighting device
according to Embodiment 2;
[0016] FIG. 6 is a time chart of an operation of the lighting
device;
[0017] FIG. 7 is a time chart of an operation of the lighting
device;
[0018] FIG. 8 is a time chart of an operation of a lighting device
according to Embodiment 3;
[0019] FIG. 9 is a time chart of an operation of the lighting
device;
[0020] FIG. 10 is a time chart of an operation of a lighting device
according to Embodiment 4;
[0021] FIG. 11 is a time chart of an operation of the lighting
device;
[0022] FIG. 12 is a schematic diagram of a headlight according to
Embodiment 5; and
[0023] FIG. 13 is a schematic diagram of a vehicle according to
Embodiment 6.
DETAILED DESCRIPTION
[0024] Embodiments described below each relate generally to
lighting devices, headlights, and vehicles, and more particularly,
to a lighting device configured to light a light source, a
headlight including the lighting device, and a vehicle including
the headlight.
Embodiment 1
[0025] As shown in FIG. 1, a lighting device 1 according to
Embodiment 1 includes a power converter 3, a bypass switch Q2, and
a controller 6. The lighting device 1 is configured to supply a DC
(direct-current) voltage and a DC current generated by the power
converter 3 to a light source (DC light source) 2 to light the
light source 2.
[0026] The light source 2 includes multiple (eight, in the example
shown in FIG. 1) light emitting diodes (LEDs) 20 electrically
connected in series. In the explanation below, a series circuit of
four LEDs 20 on a high potential side, of the multiple LEDs 20
constituting the light source 2, is referred to as a first light
source 21, and a series circuit of other four LEDs 20 on a low
potential side, of the multiple LEDs 20 is referred to as a second
light source 22.
[0027] The lighting device 1 and the light source 2 of the present
embodiment are adapted for a headlight equipped on a vehicle such
as an automobile, for example. The first light source 21 may be
used as a low-beam headlight. A combination of the first light
source 21 and the second light source 22 may be used as a main
(high-beam) headlight.
[0028] The lighting device 1 of the present embodiment includes
three input terminals (a first input terminal X1, a second input
terminal X2, and a third input terminal X3), and three output
terminals (a first output terminal Y1, a second output terminal Y2,
and a third output terminal Y3).
[0029] The first input terminal X1 is to be electrically connected
to a positive electrode of a (external) DC power source B1 via a
first switch SW1. The second input terminal X2 is to be
electrically connected to a negative electrode of the DC power
source B1. The third input terminal (signal input terminal) X3 is
to be electrically connected to the positive electrode of the DC
power source B1 via a second switch SW2. That is, the DC power
source B1 is to be electrically connected between the first input
terminal X1 and the second input terminal X2 (via the first switch
SW1).
[0030] In the present embodiment, the DC power source B1 is a
battery equipped on the vehicle. The first switch SW1 and the
second switch SW2 are situated on particular places of the vehicle
where a driver can easily operate them, for example, around a
driver's sheet.
[0031] The first output terminal Y1 is to be electrically connected
to a positive electrode of the first light source 21 (an anode of
an LED 20 on the highest potential side in the first light source
21; a first end of the first light source 21). The second output
terminal Y2 is to be electrically connected to a negative electrode
of the second light source 22 (a cathode of an LED 20 on the lowest
potential side in the second light source 22; a second end of the
second light source 22). The third output terminal Y3 is to be
electrically connected to a negative electrode of the first light
source 21 (a cathode of an LED 20 on the lowest potential side in
the first light source 21; a second end of the first light source
21) and a positive electrode of the second light source 22 (an
anode of an LED 20 on the highest potential side in the second
light source 22; a first end of the second light source 22). In
other words, the first light source 21 is to be electrically
connected between the first output terminal Y1 and the third output
terminal Y3. The second light source 22 is to be electrically
connected between the third output terminal Y3 and the second
output terminal Y2.
[0032] The power converter 3 includes a flyback DC-DC converter.
The power converter 3 includes an insulated transformer T1 (a
primary winding N1 and a secondary winding N2), a first switching
element Q1, a diode D1, a capacitor C1, and a primary current meter
30.
[0033] The primary winding N1 of the insulated transformer T1 has a
winding start end (a dotted end, hereinafter referred to as a
"first end") electrically connected to the first input terminal X1,
and a winding finish end (hereinafter referred to as a "second
end") electrically connected to the second input terminal X2 via
the first switching element Q1. The secondary winding N2 of the
insulated transformer T1 has a winding start end (a dotted end,
hereinafter referred to as a "first end") electrically connected to
the second output terminal Y2 via the diode D1 and a resistor
(shunt resistor) R3 for current measurement, and a winding finish
end (hereinafter referred to as a "second end") electrically
connected to the first output terminal Y1. The diode D1 has a
cathode electrically connected to the first end of the secondary
winding N2, and an anode electrically connected to the resistor R3.
The capacitor C1 is electrically connected between the second end
of the secondary winding N2 and the anode of the diode D1.
[0034] The first switching element Q1 is constituted by an
N-channel enhancement-type Metal-Oxide-Semiconductor Field Effect
Transistor (MOSFET). The first switching element Q1 has a drain
electrode (a first electrode) electrically connected to the second
end of the primary winding N1, and a source electrode (a second
electrode) electrically connected to the second input terminal X2.
The source electrode of the first switching element Q1 is connected
to a ground.
[0035] In the present embodiment, the first end of the primary
winding N1 and the source electrode of the first switching element
Q1 serve as a pair of input ends 31 and 32 of the power converter
3, respectively. Both ends of the capacitor C1 serve as a pair of
output ends 33 and 34 of the power converter 3. The two input ends
31 and 32 of the power converter 3 are electrically connected to
the first and second input terminals X1 and X2, respectively. The
output end 33 of the power converter 3 is electrically connected to
the first output end Y1. The output end 34 of the power converter 3
is electrically connected to the second output terminal Y2 via the
resistor R3.
[0036] The primary current meter 30 is electrically connected to a
junction of the second end of the primary winding N1 and the drain
electrode of the first switching element Q1. The primary current
meter 30 is configured to measure a current (primary current)
flowing through the first switching element Q1 by measuring a
drain-source voltage of the first switching element Q1 (namely, by
measuring an electric potential of the junction).
[0037] Whether to supply the DC voltage and DC current from the DC
power source B1 to the power converter 3 is determined in
accordance with an ON state and an OFF state of the first switch
SW1. Specifically, the DC voltage and the DC current are allowed to
be supplied from the DC power source B1 to the power converter 3
while the first switch SW1 is on. The DC voltage and the DC current
are prevented to be supplied from the DC power source B1 to the
power converter 3 while the first switch SW1 is off. In the power
converter 3, by the first switching element Q1 being periodically
turned on and off, a DC voltage (an output voltage) is generated
across the capacitor C1 (between the output ends 33 and 34 of the
power converter 3).
[0038] Specifically, during a period in which the first switching
element Q1 is on, energy is accumulated in the transformer T1 and a
current flowing through the primary winding N1 of the transformer
T1 gradually increases. During a period in which the first
switching element Q1 is off, the accumulated energy is discharged
from the secondary winding N2 of the transformer T1 and the
capacitor C1 is charged by a regeneration current flowing through
the diode D1.
[0039] The bypass switch Q2 is constituted by an N-channel
enhancement-type MOSFET. The bypass switch Q2 is electrically
connected between the second output terminal Y2 and the third
output terminal Y3. The bypass switch Q2 has a drain electrode (a
first electrode) electrically connected to the third output
terminal Y3, and a source electrode (a second electrode)
electrically connected to the second output terminal Y2. In other
words, the bypass switch Q2 is to be electrically connected in
parallel to the second light source 22 (electrically connected
between both ends of the second light source 22). The bypass switch
Q2 has: a short-circuited state (an ON-state) for creating an
electric path bypassing the second light source 22 to prevent an
output current of the power converter 3 to flow through the second
light source 22; and an open state (an OFF-state) allowing the
output current to flow through the second light source 22. The
bypass switch Q2 is turned on when a gate electrode (a control
electrode) thereof receives a drive signal S.sub.D from the driver
19. When the bypass switch Q2 is in the ON-state, the positive and
negative electrodes of the second light source 22 are
short-circuited, and thus the output current of the power converter
3 does not flow through the second light source 22. As a result,
only the first light source 21 can be operated (emit light). When
the bypass switch Q2 is in the OFF-state, the output current of the
power converter 3 is allowed to flow through the series circuit of
the first and second light sources 21 and 22, and thus both the
first and second light sources 21 and 22 can be operated (emit
light).
[0040] As shown in FIG. 1, the controller 6 includes a comparator
10, a sequential circuit 11, and a differentiation circuit 12.
[0041] The comparator 10 has a first input end electrically
connected to an output end of the primary current meter 30, a
second input end electrically connected to a processor 4, and an
output end. The comparator 10 is configured to output a high-level
output (voltage signal) from the output end while a voltage input
to the first input end is higher than a voltage input to the second
input end, and to output a low-level output from the output end
while a voltage input to the first input end is lower than a
voltage input to the second input end.
[0042] The sequential circuit 11 is composed of a set-reset
flip-flop circuit, and has a reset terminal electrically connected
to the output end of the comparator 10, a set terminal electrically
connected to the processor 4, and an output terminal electrically
connected to a gate electrode (a control electrode) of the first
switching element Q1.
[0043] The differentiation circuit 12 has an input end electrically
connected to the junction of the primary winding N1 and the first
switching element Q1, and an output end electrically connected to
the processor 4.
[0044] Hereinbelow, an operation of the power converter 3 is
explained. When the first switching element Q1 is turned on, a
current (an excitation current) flows through the primary winding
N1 of the transformer T1. When the excitation current flows, an ON
resistance of the first switching element Q1 causes a voltage drop,
and this lead to rise of the drain-source voltage of the switching
element Q1 to a high-level. The primary current meter 30 of the
power converter 3 measures the primary current flowing through the
primary winding N1 of the transformer T1. The primary current meter
30 is configured to measure the drain-source voltage of the first
switching element Q1, thereby indirectly measuring the excitation
current. The primary current meter 30 outputs a measured voltage (a
voltage proportional to the excitation current) to the comparator
10.
[0045] The comparator 10 compares the measured voltage of the
primary current meter 30 with a reference voltage Vref (described
later) supplied from the processor 4, and to output a high-level
output when the measured voltage is higher than the reference
voltage. The output of the comparator 10 is supplied to the reset
terminal of the sequential circuit 11. Specifically, when the
measured voltage of the primary current meter 30 is greater than
the reference voltage V.sub.ref, the input voltage to the reset
terminal of the sequential circuit 11 rises to a high-level, and
thus the sequential circuit 11 outputs a low-level output (voltage
signal). The output of the sequential circuit 11 is supplied to the
gate electrode of the first switching element Q1. Therefore, the
first switching element Q1, receiving the low-level output of the
sequential circuit 11, is turned off.
[0046] When the first switching element Q1 is turned off, the
energy accumulated on the primary winding N1 of the transformer T1
is discharged to the secondary side. When the discharge of the
energy finishes, the drain-source voltage of the first switching
element Q1 falls to a low-level. The falling edge of the
drain-source voltage is detected by the processor 4 (ON-pulse
generation section 47) via the differential circuit 12. Upon
detecting the falling edge of the drain-source voltage via the
differentiation circuit 12, the processor 4 (the ON-pulse
generation section 47) outputs a pulse signal to the set terminal
of the sequential circuit 11. Upon the input voltage to the set
terminal rising to a high-level by the pulse signal from the
processor 4, the sequential circuit 11 outputs a high-level output
to turn on the first switching element Q1 again. Therefore, the
power converter 3 of the present embodiment is controlled in
accordance with a Boundary Current Mode.
[0047] The lighting device 1 is configured to, in a normal state,
execute a constant current control of keeping a current flowing
through the light source 2 constant, to thereby light the light
source 2. The constant current control is executed by the
controller 6 including the processor (microcontroller) 4 as a main
component. The controller 6 further includes a voltage meter 13, a
current meter 14, resistors R1 to R3, and a driver 19, as shown in
FIG. 1.
[0048] As shown in FIG. 1, a series circuit of the voltage divider
resistors R1 and R2 is electrically connected between the first and
second output terminals Y1 and Y2 (between the output ends 33 and
34 of the power converter 3). Also, the resistor R3 for current
measurement is electrically connected between the output end 34, on
a low potential side, of the power converter 3 (a junction of the
anode of the diode D1 and the capacitor C1) and the second output
terminal Y2. Specifically, the resistor R3 is electrically
connected between a junction of the output end 34 of the power
converter 3 and the series circuit of the resistors R1 and R2, and
the second output terminal Y2.
[0049] The voltage meter 13 of the lighting device 1 is configured
to measure a divided voltage of the output voltage of the power
converter 3 (a first measurement voltage) obtained by dividing the
output voltage of the power converter 3 by the voltage divider
resistors R1 and R2, and to output, to the processor 4, the first
measurement voltage corresponding to the output voltage of the
power converter 3. The current meter 14 of the lighting device 1 is
configured to measure a voltage across the resistor R3 (a second
measurement voltage) that corresponds to a current supplied from
the lighting device 1 to the light source 2 (an output current of
the power converter 3), and to output the second measurement
voltage to the processor 4.
[0050] The processor 4 executes various programs with a built-in
central processing unit (CPU) to realize various functions. The
processor 4 includes a built-in or an external memory storing such
programs. As shown in FIG. 1, the processor 4 in the present
embodiment includes a first averaging section 40, a second
averaging section 41, a current instruction section 42, a
comparison operation section 43, a switch control section 44, a
threshold output section 45, an abnormal state determining section
46, and the ON-pulse generation section 47 (these sections
represent functions of program modules realized by the hardware
components of the processor 4).
[0051] The first averaging section 40 is configured to calculate an
average of the first measurement voltage supplied from the voltage
meter 13. For example, the first averaging section 40 is configured
to perform analog-digital conversion of the first measurement
voltage to obtain a corresponding first measurement voltage value,
and to calculate a moving average of the first measurement voltage
value.
[0052] The second averaging section 41 is configured to calculate
an average of the second measurement voltage supplied from the
current meter 14. For example, the second averaging section 41 is
configured to perform analog-digital conversion of the second
measurement voltage to obtain a corresponding second measurement
voltage value, and to calculate a moving average of the second
measurement voltage value.
[0053] The current instruction section 42 is configured to read out
a target value of the output current from the memory of the
processor 4, and to send the target value to the comparison
operation section 43.
[0054] The comparison operation section 43 is configured to compare
the average value of the output current (specifically the average
value of the second measurement voltage value) obtained by the
second averaging section 41 with the target value supplied from the
current instruction section 42, and to calculate a primary current
instruction value based on a difference between the target value
and the average value. For example, the comparison operation
section 43 is configured to generate a comparatively small primary
current value when the average value is larger than the target
value, and to generate a comparatively large primary current value
when the average value is smaller than the target value. The
processor 4 is configured to perform digital-analog conversion of
the primary current instruction value generated by the comparison
operation section 43 to generate a reference voltage V.sub.ref, and
to output the reference voltage V.sub.ref to the comparator 10.
[0055] The reference voltage V.sub.ref is decreased with a decrease
in the primary current instruction value, and hence the ON-period
of the first switching element Q1 is shortened, and as a result the
output current decreases. The reference voltage V.sub.ref is
increased with an increase in the primary current instruction
value, and hence the ON-period of the first switching element Q1 is
prolonged, and as a result the output current increases. With this
procedure, the processor 4 controls the switching element Q1 to
realize the constant current control on the power converter 3. In
other words, the processor 4 performs a feedback control by
adjusting (changing) the primary current instruction value (the
reference voltage V.sub.ref) so that the magnitude of the current
supplied to the light source 2 is kept equal to the target value of
the current instruction section 42.
[0056] The switch control section 44 is configured to output a
switch control signal S.sub.SC according to a detection result of a
second power supply detector 16. The second power supply detector
16 has an input end electrically connected to the third input
terminal X3, and an output end electrically connected to the
processor 4. The second power supply detector 16 is configured to
output a second detection signal S.sub.2 while a voltage of the
third input terminal X3 (difference in potential between the ground
and the third input terminal X3) is equal to or greater than a
predetermined threshold voltage, and not output the second
detection signal S.sub.2 while the voltage of the third input
terminal X3 is lower than the predetermined threshold voltage. In
other words, the second power supply detector 16 detects an
ON-state and an OFF-state of the second switch SW2 based on a
comparison result between the voltage of the third input terminal
X3 and the predetermined threshold voltage. The switch control
section 44 does not output the switch control signal S.sub.SC while
the second detection signal S2 is supplied from the second power
supply detector 16, whereas the switch control section 44 outputs
the switch control signal S.sub.SC while the second detection
signal S2 is not supplied from the second power supply detector 16.
The driver 19 outputs a drive signal S.sub.D to the gate electrode
of the bypass switch Q2 to turn on the bypass switch Q2 while the
switch control signal S.sub.SC is supplied. The driver 19 does not
output the drive signal S.sub.D to turn off the bypass switch while
the switch control signal S.sub.SC is not supplied.
[0057] In short, the bypass switch Q2 is kept off by the processor
4 while the second switch SW2 is on. In this case, both the first
light source 21 and the second light source 22 are allowed to be
lit. The bypass switch Q2 is kept on by the processor 4 while the
second switch SW2 is off. In this case, only the first light source
21 is allowed to be lit.
[0058] In other words, the third input terminal (signal input
terminal) X3 is configured to receive a first instruction signal
S.sub.I1 and a second instruction signal S.sub.I2. The controller 6
is configured to keep the bypass switch Q2 off while the first
instruction signal S.sub.I1 is supplied through the third input
terminal X3 (while the voltage of the third input terminal X3 is
equal to or greater than the predetermined threshold voltage; while
the second detection signal S.sub.2 is supplied from the second
power supply detector 16 to the processor 4). The controller 6 is
configured to keep the bypass switch Q2 on while the second
instruction signal S.sub.I2 is supplied through the third input
terminal X3 (while the voltage of the third input terminal X3 is
smaller than the predetermined threshold voltage; while the second
detection signal S.sub.2 is not supplied from the second power
supply detector 16 to the processor 4).
[0059] The ON-pulse generation section 47 is configured to output a
pulse signal to the set terminal of the sequential circuit 11 upon
detecting the falling edge of the drain-source voltage of the first
switching element Q1 through the differentiation circuit 12. The
ON-pulse generation section 47 of the present embodiment is
configured to also output a pulse signal to the set terminal of the
sequential circuit 11 when a predetermined suspension time elapses
after outputting a pulse signal last time (namely, configured to
output the pulse signal every time the suspension time elapses).
With this configuration, the first switching element Q1 can be
turned on even if the processor 4 fails to detect the falling edge
of the drain-source voltage due to failure of the differentiation
circuit 12, for example.
[0060] Preferably, the processor 4 is configured to determine
whether to start the operation of the power converter 3, based on a
voltage measured by a first power supply detector 15. The first
power supply detector 15 has an input end electrically connected to
the first input terminal X1, and an output end electrically
connected to the processor 4. The first power supply detector 15 is
configured to measure a voltage of the first input terminal X1
(difference in potential between the first input terminal X1 and
the second input terminal X2 (ground)), and to output, to the
processor 4, a first detection signal S.sub.1 indicative of the
measured voltage. Preferably, the processor 4 starts the operation
of the power converter 3 when a signal level of the first detection
signal S.sub.1 is within a predetermined operation permitted range,
and does not start the operation of the power converter 3 when the
signal level of the first detection signal S.sub.1 is out of the
predetermined operation permitted range.
[0061] The processor 4 operates with a control power voltage
generated by a control power generator 17. The control power
generator 17 is configured to generate the control power voltage
using the DC voltage supplied from the DC power source B1 through
the first switch SW1.
[0062] In the activation process of the lighting device 1, the
first switch SW1 is turned on, and the control power voltage is
generated by the control power generator 17, and then the processor
4 is activated with the control power voltage. If the signal level
of the first detection signal S.sub.1 from the first power supply
detector 15 is within the operation permitted range, the processor
4 outputs a pulse signal to the set terminal of the sequential
circuit 11 from the ON-pulse generation section 47. Switching
operation of the first switching element Q1 (operation of the power
converter 3) is thus started.
[0063] As shown in FIG. 1, the lighting device 1 of the present
embodiment includes an interrupter 18. The interrupter 18 includes
a comparator 180, input resistors R4 and R5, and a third switching
element Q3.
[0064] The comparator 180 has a non-inverting input terminal (a
first terminal) to receive the first measurement voltage from the
voltage meter 13 through the input resistor R4. The comparator 180
has an inverting input terminal (a second terminal) to receive an
excess-voltage threshold (a first type threshold) from the
threshold output section 45 of the processor 4. The comparator 45
is configured to compare the first measurement voltage with the
excess-voltage threshold. The comparator 45 outputs a high-level
output (voltage signal) while the first measurement voltage is
equal to or greater than the excess-voltage threshold, and outputs
a low-level output while the first measurement voltage is less than
the excess-voltage threshold.
[0065] The third switching element Q3 is constituted by an
N-channel enhancement-type (normally off type) MOSFET. The third
switching element Q3 has a drain electrode (a first electrode)
electrically connected to the set terminal of the sequential
circuit 11, a source electrode (a second electrode) electrically
connected to the ground, and a gate electrode (a control electrode)
electrically connected to an output terminal of the comparator
180.
[0066] While the output of the comparator 180 is in a low-level,
the third switching element Q3 is kept in an OFF-state. The pulse
signal from the processor 4 is therefore allowed to be input to the
set terminal of the sequential circuit 11. While the output of the
comparator 180 is in a high-level (while the first measurement
voltage is equal to or greater than the excess-voltage threshold),
the third switching element Q3 is on. In this case, the set
terminal of the sequential circuit 11 is grounded through the third
switching element Q3, and thus the pulse signal from the processor
4 cannot be supplied to the set terminal of the sequential circuit
11. Therefore, the output of the sequential circuit 11 is not
switched to the high-level. As a result, the first switching
element Q1 is kept turned off and the operation of the power
converter 3 is stopped.
[0067] The lighting device 1 includes the interrupter 18, and
accordingly it is possible to prevent an excess increase in the
output voltage of the power converter 3.
[0068] Incidentally, when the first switching element Q1 is turned
off, the first measurement voltage (the output voltage of the power
converter 3) gradually decreases. When the first measurement
voltage decreases and becomes less than the excess-voltage
threshold, the output of the comparator 180 is switched to the
low-level (therefore, the third switching element Q3 is turned
off). As described above, the processor 4 of the present embodiment
is configured to output a pulse signal when the predetermined
suspension time elapses from a time when the processor 4 outputs a
pulse signal last time, even if the processor 4 fails to detect the
falling edge of the drain-source voltage. Therefore, after the
output of the interrupter 18 is switched to the low-level, the
first switching element Q1 is turned on again by a pulse signal
from the processor 4. The output of the interrupter 18 is therefore
repeatedly switched between the high-level and the low level until
a cause of an increase in the output voltage of the power converter
3, such as an open circuit failure of the light source 2, is
resolved. Therefore, the output voltage of the power converter 3 is
maintained around a particular voltage (an excess voltage) at which
the first measurement voltage equals to the excess-voltage
threshold.
[0069] The excess voltage of the output voltage of the power
converter 3 possibly causes a continuous severe stress on the light
source 2, the bypass switch Q2, the processor 4, and the like. In
view of this, the processor 4 of the present embodiment includes
the abnormal state determining section 46. The abnormal state
determining section 46 is configured to compare the average of the
first measurement voltage from the first averaging section 40 with
a high-voltage threshold (second type threshold) from the threshold
output section 45, and to count (measure) a time during which the
average of the first measurement voltage is kept equal to or
greater than the high-voltage threshold, as a duration time. When
the duration time reaches predetermined upper limit time (150 ms,
for example), the abnormal state determining section 46 (the
processor 4) performs a process for terminating the operation of
the power converter 3. For example, the abnormal state determining
section 46 may cause the comparison operation section 43 to
generate a primary current instruction value of around 0. As a
result, the first switching element Q1 is kept in the OFF-state.
With this configuration, the processor 4 can stop the operation of
the power converter 3 without delay when a voltage (an excess
voltage) higher than a rated voltage of the light source 2 is
continuously applied to the light source 2, and thus can protect
the light source 2, the bypass switch Q2, the processor 4, and the
like.
[0070] As shown in FIG. 1, preferably, the lighting device 1
includes a first filter 50 and a second filter 51. The first filter
50 is interposed between the voltage meter 13 and the interrupter
18. The second filter 51 is interposed between the voltage meter 13
and the processor 4 (the first averaging section 40). Preferably,
each of the first filter 50 and the second filter 51 is constituted
by a low-pass filter, and is configured to remove harmonic noise
component contained in the first measurement voltage of the voltage
meter 13. The first measurement voltage is filtered by the first
filter 50, and is supplied to the interrupter 18. The first
measurement voltage is also filtered by the second filter 51, and
is supplied to the first averaging section 40. Preferably, a time
constant of the low-pass filter of the first filter 50 is
sufficiently smaller than a time constant of the low-pass filter of
the second filter 51. The processor 4 averages the first
measurement voltage by the first averaging section 40, and further
the duration time during which the average of the first measurement
voltage is equal to or greater than the high-voltage threshold is
counted. Therefore, it is preferable that the time constant of the
low-pass filter of the second filter 51 be set to be comparatively
large, with emphasis on a noise reduction property rather than a
responsibility. Contrary, regarding the interrupter 18, the time
constant of the low-pass filter of the first filter 50 is
preferably set to be comparatively small, with emphasis on the
responsibility rather than the noise reduction property.
[0071] Incidentally, in a case where an increase in the output
voltage of the power converter 3 is caused by a bad connection
between any of the output terminals Y1 to Y3 of the lighting device
1 and the light source 2, a connection state may be changed between
a correct connection state and an incorrect connection state due to
external factors such as vibration. In this case, if the connection
state recovers from the incorrect connection state to the correct
connection state before the duration time during which the average
of the first measurement voltage is equal to or greater than the
high-voltage threshold reaches the upper limit, an excess voltage
(a voltage at which the first measurement voltage equals to the
excess-voltage threshold, for example) higher than the rated
voltage of the light source 2 would be applied to the light source
2. As a result, a rush current depending on a difference between
the excess voltage and the rated voltage may flow into the LEDs 20.
In other words, after an increase in the output voltage of the
power converter 3 resulting from a disconnection of the light
source 2 from any of the output terminals Y1 to Y3, when the light
source 2 is correctly connected to the output terminals Y1 to Y3,
an excess voltage higher than the rated voltage may be applied to
the light source 2. Particularly, in a configuration in which the
excess-voltage threshold is set to be greater than the sum of rated
voltages of the light sources 21 and 22 and in a case where only
the first light source 21 is turned on (in a case where the bypass
switch Q2 is turned on), if a connection state recovers to the
correct connection state from the incorrect connection state, a
significantly large rush current possibly flows into the first
light source 21 and the bypass switch Q2.
[0072] In view of the above, the lighting device 1 of the present
embodiment is configured to change the excess-voltage threshold
depending on whether the current state is a state where only the
first light source 21 is allowed to be lit (hereinafter, referred
to as "low-beam state") or a state where both the first and second
light sources 21 and 22 are allowed to be lit (hereinafter,
referred to as "main-beam state"). Specifically, the threshold
output section 45 of the processor 4 sets a first threshold voltage
TH1 as the excess-voltage threshold while the second detection
signal S.sub.2 is supplied (in the main-beam state; while the first
instruction signal S.sub.I1 is supplied), and sets a second
threshold voltage TH2 (<the first threshold voltage TH1) as the
excess-voltage threshold while the second detection signal S.sub.2
is not supplied (in the low-beam state; while the second
instruction signal S.sub.I2 is supplied). The first threshold
voltage TH1 is set to be larger than the sum of the rated voltages
of the light sources 21 and 22. The second threshold voltage TH2 is
set to be larger than the rated voltage of the first light source
21 but smaller than the sum of the rated voltages of the light
sources 21 and 22. In a specific example in which the rated
voltages of the light sources 21 and 22 are each 15.+-.3 [V], the
first threshold voltage TH1 may be set to 41.times.(a division
ratio of the voltage divider resistors R1 and R2) [V], and the
second threshold voltage TH2 may be set to 23.times.(the division
ratio of the voltage divider resistors R1 and R2) [V]. The division
ratio of the voltage divider resistors R1 and R2 may be defined as
r2/(r1+r2), where r1 and r2 denote resistance values of the
resistors R1 and R2, respectively. However, the first threshold
voltage TH1 and the second threshold voltage TH2 are not limited
thereto.
[0073] Preferably, the threshold output section 45 changes not only
the excess-threshold but also the high-voltage threshold depending
on whether the current state is the low-beam state or the main-beam
state. Specifically, the threshold output section 45 sets a third
threshold voltage TH3 as the high-voltage threshold in the
main-beam state, and sets a fourth threshold voltage TH4 (<the
third threshold voltage TH3) as the high-voltage threshold in the
low-beam state, preferably. The third threshold voltage TH3 is set
to be larger than the sum of the rated voltages of the light
sources 21 and 22 but smaller than the first threshold voltage TH1.
The fourth threshold voltage TH4 is set to be larger than the rated
voltage of the first light source 21 but smaller than the second
threshold voltage TH2. In the specific example in which the rated
voltages of the light sources 21 and 22 are each 15.+-.3 [V], the
first threshold voltage TH1 is set to 41.times.(the division ratio
of the voltage divider resistors R1 and R2) [V], and the second
threshold voltage TH2 is set to 23.times.(the division ratio of the
voltage divider resistors R1 and R2) [V], the third threshold
voltage TH3 may be set to 38.times.(the division ratio of the
voltage divider resistors R1 and R2) [V], and the fourth threshold
voltage TH4 may be set to 20.times.(the division ratio of the
voltage divider resistors R1 and R2) [V]. However, the first to
fourth threshold voltages TH1 to TH4 are not limited thereto.
[0074] With reference to the flow chart of FIG. 2 and the time
chart of FIG. 3, an operation of the lighting device 1 of the
present embodiment (particularly, an operation of the lighting
device 1 in a case where the open circuit failure occurs in the
light source 2 and this leads to an increase in the output voltage
of the power converter 3) will be explained. FIG. 2 shows a flow
chart illustrating the operation (processing) of the processor
4.
[0075] When the first switch SW1 is turned on (t=t1 in FIG. 3), the
processor 4 starts performing the constant current control for
keeping the output current of the power converter 3 equal to the
target value (corresponding to a rated current of the light source
2) based on the above-described manner. The processor 4 always
monitors whether the second detection signal S.sub.2 is present or
absent (whether the signal has the high-level or the low-level) (S1
in FIG. 2). While the second detection signal S.sub.2 is supplied
to the processor 4 (while the first instruction signal S.sub.I1 is
supplied), the threshold output section 45 sets the first threshold
voltage TH1 as the excess-voltage threshold and sets the third
threshold voltage TH3 as the high-voltage threshold (S2 in FIG. 2).
When no fault occurs in the light source 2 and the lighting device
1, the output voltage of the power converter 3 is kept at a voltage
(a first rated voltage) which is equal to the sum of the rated
voltages of the first and second light sources 21 and 22 as well as
smaller than the third threshold voltage TH3 (see FIG. 3).
[0076] When at least one of the first and second light sources 21
and 22 has an open circuit failure (t=t2), the output voltage of
the power converter 3 starts increasing due to the constant current
control performed by the processor 4 (see FIG. 3). When the output
voltage of the power converter 3 increases up to a voltage at which
the first measurement voltage equals to the excess-voltage
threshold (i.e., the first threshold voltage TH1) (t=t4), the
interrupter 18 stops the operation of the power converter 3. Then
the output of the interrupter 18 is repeatedly switched between the
high-level and the low-level as described above when the cause
(open circuit failure in the second light source 22, for example)
of the increase in the output voltage is not resolved. The output
voltage of the power converter 3 is thus kept around an excess
voltage at which the first measurement voltage equals to the
excess-voltage threshold (the first threshold voltage TH1) (see
FIG. 3).
[0077] The processor 4 normally compares the average of the first
measurement voltage with the high-voltage threshold (the third
threshold voltage TH3) (S4 in FIG. 2). In a period in which the
first measurement voltage is less than the high-voltage threshold
(the third threshold voltage TH3), the processor 4 resets (clear)
the measured duration time (S5 in FIG. 2). When the average of the
first measurement voltage increases up to the high-voltage
threshold (the third threshold voltage TH3) due to an increase in
the output voltage of the power converter 3 (t=t3), the processor 4
starts counting (measuring) the duration time (S6 in FIG. 2). The
processor 4 compares the duration time with an upper limit time TU1
(TU1=150 ms, for example) while counting the duration time (S7 in
FIG. 2). When the duration time is less than the upper limit time
TU1, the processor 4 returns to the step S4 and compares the
average of the first measurement voltage with the high-voltage
threshold (the third threshold voltage TH3). When the duration time
reaches the upper limit time TU1 (t=t5), the processor 4 performs
the process for terminating the operation of the power converter 3
(S8 in FIG. 2).
[0078] While the second detection signal S.sub.2 is not supplied to
the processor 4 (while the second instruction signal S.sub.I2 is
supplied) (t=t6), the threshold output section 45 sets the second
threshold voltage TH2 as the excess-voltage threshold and sets the
fourth threshold voltage TH4 as the high-voltage threshold (S3 in
FIG. 2). If no fault occurs in the light source 2 and the lighting
device 1, the output voltage of the power converter 3 is kept at a
voltage (a second rated voltage) which is equal to the rated
voltage of the first light source 21 but smaller than the fourth
threshold voltage TH4 (see FIG. 3).
[0079] When the first light source 21 has an open circuit failure
(t=t7), the output voltage of the power converter 3 starts
increasing due to the constant current control performed by the
processor 4 (see FIG. 3). When the output voltage of the power
converter 3 increases up to a voltage at which the first
measurement voltage equals to the excess-voltage threshold (i.e.,
the second threshold voltage TH2) (t=t8), the interrupter 18 stops
the operation of the power converter 3. The output voltage of the
power converter 3 is thus kept around an excess voltage at which
the first measurement voltage equals to the excess-voltage
threshold (the second threshold voltage TH2) (see FIG. 3).
[0080] The processor 4 normally compares the average of the first
measurement voltage with the high-voltage threshold (the fourth
threshold voltage TH4) (S4 in FIG. 2). In a period in which the
first measurement voltage is less than the high-voltage threshold
(the fourth threshold voltage TH4), the processor 4 resets (clear)
the measured duration time (S5 in FIG. 2). When the average of the
first measurement voltage increases up to the high-voltage
threshold (the fourth threshold voltage TH4) due to an increase in
the output voltage of the power converter 3 (t=t3), the processor 4
starts counting (measuring) the duration time (S6 in FIG. 2). The
processor 4 compares the duration time with an upper limit time TU2
(TU2=150 ms, for example) while counting the duration time (S7 in
FIG. 2). If the duration time is less than the upper limit TU2, the
processor 4 returns to the step S4 to compares the average of the
first measurement voltage with the high-voltage threshold (the
fourth threshold voltage TH4). When the duration time reaches the
upper limit time TU2 (t=t9), the processor 4 performs the process
for terminating the operation of the power converter 3 (S8 in FIG.
2).
[0081] With reference to the time chart of FIG. 4, an operation of
the lighting device 1 in a case where the bypass switch Q2 comes to
have the open circuit failure (the bypass switch Q2 is latched at
the OFF-state due to failure). While the second switch SW2 is on,
the lighting device 1 would normally operate (t=t1.about.t2)
regardless of the open circuit failure of the bypass switch Q2.
While the second switch SW2 is off, the bypass switch Q2 having the
open circuit failure cannot be switched from the open state to the
short-circuited state even when receiving the drive signal SD. In
this case, the threshold output section 45 sets the second
threshold voltage TH2 as the excess-voltage threshold, and sets the
fourth threshold voltage TH4 as the high-voltage threshold, because
the second detection signal S2 is not supplied.
[0082] In this case, immediately after the process 4 starts the
constant current control (t=t3), the first measurement voltage
increases and exceeds the excess-voltage threshold (the second
threshold voltage TH2) (t=t4). The output voltage of the power
converter 3 is thus maintained around a voltage at which the first
measurement voltage equals to the excess-voltage threshold (the
second threshold voltage TH2). When a time (duration time) during
which the first measurement voltage is maintained around the
excess-voltage threshold (the second threshold voltage TH2) reaches
the upper limit time TU2, the processor 4 performs the process for
terminating the operation of the power converter 3 (t=t5). A driver
of the vehicle therefore can recognize occurrence of the failure of
the lighting device 1 and the light source 2, because the light
source 2 does not emit light even when the first switch SW1 is
turned on. In this case, by turning on both the first and second
switches SW1 and SW2, the first and second light sources 21 and 22
can be lit by the lighting device 1. The driver therefore can drive
the vehicle to a desired safe place (one's home or automobile
repair shop) at night even when the lighting device 1 or the light
source 2 are failed.
[0083] As described above, the lighting device 1 of the present
embodiment is configured to change the excess-voltage threshold
between the first threshold voltage TH1 and the second threshold
voltage TH2 according to whether the current situation is a
situation where both the first and second light sources 21 and 22
are to be lit or another situation where only the first light
source 21 is to be lit (the second threshold voltage TH2<the
first threshold voltage TH1). It is accordingly possible to
suppress the magnitude of the rush current that possibly flows into
the light source 2 in a recovering time to a correctly connected
state, in comparison with a configuration in which the
excess-voltage threshold is fixed to the first threshold voltage
TH1. The lighting device 1 of the present embodiment uses the
second threshold voltage TH2 lower than the first threshold voltage
TH1 as the excess-voltage threshold, in a case where only the first
light source 21 is allowed to be lit. It is accordingly possible to
detect an abnormal output voltage of the power converter 3 more
reliably. Consequently, the lighting device 1 of the present
embodiment can suppress an occurrence of a failure that possibly
damages the light source 2, and can detect an occurrence of an
abnormal output voltage of the power converter 3 more reliably. It
should be noted that the upper limit time TU1 and TU2, to be
compared with the duration time, may be the same or different from
each other.
[0084] As described above, the lighting device 1 of the present
embodiment includes the power converter 3, the bypass switch Q2,
the controller 6 (the processor 4, the comparator 10, the
sequential circuit 11, the differentiation circuit 12, the
interrupter 18 and the driver 19). The controller 6 includes the
voltage meter 13. The lighting device 1 is configured to supply DC
voltage and DC current generated by the power converter 3 to the
light source 2 to light (operate) the light source 2. The light
source 2 includes the first light source 21 and the second light
source 22. The first light source 21 and the second light source 22
are to be electrically connected in series between the output ends
33 and 34 of the power converter 3 (between the first output
terminal Y1 and the second output terminal Y2). The bypass switch
Q2 is to be electrically connected in parallel to the second light
source 22. The bypass switch Q2 is configured to be switched
between the short-circuited state for bypassing the second light
source 22 to prevent an output current of the power converter 3 to
flow through the second light source 22, and the open state for
allowing the output current to flow through the second light source
22. The power converter 3 includes the DC-DC converter that has at
least one switching element (the first switching element) Q1. The
controller 6 is configured to switch the bypass switch Q2 between
the short-circuited state and the open state. The controller 6 is
configured to control the switching element Q1 to adjust the output
current of the power converter 3. The voltage meter 13 is
configured to measure an output voltage of the power converter 3 or
a divided voltage obtained by dividing the output voltage of the
power converter 3. The controller 6 is configured to, while keeping
the bypass switch in the open state, stop the operation of the
power converter 3 by controlling the switching element Q1 when
determining that a measured voltage of the voltage meter 13 (the
first measurement voltage) is equal to or greater than the
predetermined first threshold voltage TH1. The controller 6 is
configured to, while keeping the bypass switch in the
short-circuited state, stop the operation of the power converter 3
by controlling the switching element Q1 when determining that the
measured voltage of the voltage meter 13 is equal to or greater
than the predetermined second threshold voltage TH2. The second
threshold voltage TH2 is set to be larger than the second rated
voltage that corresponds to a rated value of the output voltage of
the power converter 3 under a condition where the bypass switch Q2
is kept in the short-circuited state but smaller than the first
rated voltage that corresponds to a rated value of the output
voltage of the power converter 3 under a condition where the bypass
switch Q2 is kept in the open state. The first threshold voltage
TH1 is set to be larger than the first rated voltage.
[0085] The lighting device of the present embodiment has the above
described configuration and thus is configured to change the
threshold voltage of the output voltage of the power converter 3
depending on the state of the bypass switch Q2. It is accordingly
possible to detect an occurrence of abnormal output voltage of the
power converter 3 more reliably while avoiding an occurrence of a
failure.
[0086] In the lighting device 1 of the present embodiment, the
controller 6 is configured as follows. The controller 6 is
configured to stop the operation of the power converter 3 by
controlling the switching element when determining that a state
where the measured voltage of the voltage meter 13 is equal to or
greater than the predetermined third threshold voltage TH3 or the
predetermined fourth threshold voltage TH4 continues for the
predetermined first upper limit time TU1 or the predetermined
second upper limit time TU2. While keeping the bypass switch Q2 in
the open state, the controller 6 selects the third threshold
voltage TH3 and the first upper limit time TU1. While keeping the
bypass switch Q2 in the short-circuited state, the controller 6
selects the fourth threshold voltage TH4 and the second upper limit
time TU2. The third threshold voltage TH3 is set to be larger than
the first rated voltage but smaller than the first threshold
voltage TH1. The fourth threshold voltage TH4 is set to be larger
than the second rated voltage but smaller than the second threshold
voltage TH2.
[0087] The lighting device 1 of the present embodiment has the
above described configuration, and accordingly it is possible to
avoid long time application of the excess voltage on the light
source 2 and the bypass switch Q2.
Embodiment 2
[0088] A lighting device 1 according to Embodiment 2 has the same
circuit structure as the lighting device according to Embodiment 1
as shown in FIG. 1. Therefore, detailed explanation and
illustration of the circuit structure of the lighting device 1 of
the present embodiment are omitted for sake of brevity.
[0089] The lighting device 1 of the present embodiment is
characterized by changing the excess-voltage threshold and the
high-voltage threshold after an elapse of a predetermined wait time
period from a time when a bypass switch Q2 is turned on.
[0090] With reference to the flow chart of FIG. 5 and the time
charts of FIGS. 6 and 7, operations of the lighting device 1 of the
present embodiment will be explained. FIG. 5 shows the flow chart
illustrating the operation (processing) of a processor 4.
[0091] When a first switch SW1 is turned on (t=t1 in FIGS. 6 and
7), the processor 4 starts performing a constant current control
for keeping an output current of a power converter 3 equal to a
target value (corresponding to a rated current of a light source 2)
based on the above-described manner.
[0092] With reference to FIG. 6, while a second detection signal
S.sub.2 is supplied to the processor 4 (while a first instruction
signal S.sub.I1 is supplied), a threshold output section 45 sets a
first threshold voltage TH1 as the excess-voltage threshold and
sets a third threshold voltage TH3 as the high-voltage threshold.
If no fault occurs in the light source 2 and the lighting device 1,
an output voltage of the power converter 3 is kept at a first rated
voltage.
[0093] When a second switch SW2 is turned off, the second power
supply detector 16 stops outputting the second detection signal S2,
and as a result a switch control section 44 outputs a switch
control signal S.sub.SC. The driver 19 starts outputting a drive
signal S.sub.D to turn on the bypass switch Q2 when the switch
control signal S.sub.SC is supplied (t=t2 in FIG. 6).
[0094] The processor 4 waits an elapse of the predetermined wait
time period TW (S3 in FIG. 5) from a time when supply of the second
detection signal S2 is stopped (t=t2 in FIG. 6). Upon the elapse of
the wait time period TW being detected (t=t3 in FIG. 6), the
threshold output section 45 of the processor 4 sets second and
fourth threshold voltages TH2 and TH4 as the excess-voltage
threshold and the high-voltage threshold, respectively (S4 in FIG.
5).
[0095] With reference FIG. 7, while the second detection signal
S.sub.2 is not supplied to the processor 4 (while a second
instruction signal S.sub.I2 is supplied), the threshold output
section 45 sets the second threshold voltage TH2 as the
excess-voltage threshold and sets the fourth threshold voltage TH4
as the high-voltage threshold. If no fault occurs in the light
source 2 and the lighting device 1, the output voltage of the power
converter 3 is kept at a second rated voltage.
[0096] When the second switch SW2 is turned on, the second power
supply detector 16 starts outputting the second detection signal S2
to the processor 4, and as a result the switch control section 44
stops outputting the switch control signal S.sub.SC. The driver 19
stops outputting the drive signal S.sub.D to turn off the bypass
switch Q2 when supply of the switch control signal S.sub.SC is
stopped (t=t2 in FIG. 7). Upon receiving the second detection
signal S.sub.2, the threshold output section 45 of the processor 4
sets the first and third threshold voltages TH1 and TH3 as the
excess-voltage threshold and the high-voltage threshold,
respectively (S2 in FIG. 5) without waiting the elapse of the wait
time period TW. Note that steps S5 to S9 in FIG. 5 are the same as
the steps S4 to S8 in FIG. 2, and thus explanation thereof are
omitted.
[0097] As shown in a period from t2 to t3 in FIG. 6 and a period
from t2 to t3 in FIG. 7, the output voltage of the power converter
3 (specifically, a first measurement voltage) measured with a
voltage meter 13 varies gradually due to the delay in outputting
the driver signal S.sub.D by the driver 19, transition time of the
bypass switch, and the like. Therefore, in a configuration in which
the threshold output section 45 changes the excess-voltage
threshold and the high-voltage threshold in synchronization with a
change in the second detection signal S.sub.2 in a similar manner
to Embodiment 1, the first measurement voltage may temporarily
excess the excess-voltage threshold and the lighting device 1 may
temporality turn off the light source 2.
[0098] In the lighting device 1 of the present embodiment, the
threshold output section 45 does not change the excess-voltage
threshold from the first threshold voltage TH1 to the second
threshold voltage TH2 until the wait time period TW elapses after
the processor 4 turns off the bypass switch Q2 in response to the
second detection signal S.sub.2. Therefore, the interrupter 18 does
not stop the operation of the power converter 3 during a period in
which the output voltage of the power converter 3 gradually
decrease (see FIG. 6). Therefore, undesired temporal turning off of
the light source 2 can be avoided.
[0099] In a case where the processor 4 turns off the bypass switch
Q2 in response to the second detection signal S2, the threshold
output section 45 changes the excess-voltage threshold from the
second threshold voltage TH2 to the first threshold voltage TH1
without waiting the elapse of the wait time period TW. Therefore,
the interrupter 18 does not stop the operation of the power
converter 3 during a period in which the output voltage of the
power converter 3 gradually increases (see FIG. 7). Therefore,
undesired temporal turning off of the light source 2 can be
avoided.
[0100] The wait time period TW is set to be comparable to a time
period required for the output voltage of the power converter 3 to
change from a second rated voltage to a first rated voltage. The
wait time period TW is set to around 30 ms, preferably.
[0101] As described above, in the lighting device 1 of the present
embodiment, the controller 6 is configured to, during the wait time
period TW, stop the operation of the power converter 3 by
controlling the switching element Q1 when determining that the
measured voltage of the voltage meter 13 (the first measurement
voltage) is equal to or greater than the first threshold voltage
TH1. The wait time period TW is defined as a predetermined period
of time after the bypass switch Q2 is switched from the open state
to the short-circuited state or from the short-circuited state to
the open state.
[0102] The lighting device 1 of the present embodiment has the
above described configuration, and accordingly it is possible to
reduce the possibility of undesired temporal turning off of the
light source 2 during a period in which the output voltage of the
power converter 3 changes.
Embodiment 3
[0103] A lighting device 1 according to Embodiment 3 has the same
circuit structure as the lighting device according to Embodiment 1
as shown in FIG. 1. Therefore, detailed explanation and
illustration of the circuit structure of the lighting device 1 of
the present embodiment are again omitted.
[0104] The lighting device 1 of the present embodiment is
characterized in configurations of a driver 19 and a switch control
section 44. The driver 19 of the present embodiment includes a
low-pass filter such as a CR integration circuit for example, and
is configured to allow a drive signal S.sub.D to pass through the
low-pass filter to drive (turn on and off) a bypass switch Q2 by
the filtered drive signal S.sub.D.
[0105] The switch control section 44 of the present embodiment is
configured to output a switch control signal S.sub.SC having a form
of a pulse width modulation signal. The switch control section 44
is configured to, upon detecting a falling edge of a second
detection signal S.sub.2 of a second power supply detector 16,
gradually increase a duty cycle of the switch control signal
S.sub.SC from 0% to 100%. Also, the switch control section 44 is
configured to, upon detecting a rising edge of the second detection
signal S2 of the second power supply detector 16, gradually
decrease the duty cycle of the switch control signal S.sub.SC from
100% to 0%.
[0106] While the duty cycle of the switch control signal S.sub.SC
increases from 0% to 100%, the drive signal S.sub.D of the driver
19 increases gradually from 0 [V] to a predefined voltage
(corresponding to a gate voltage of the bypass switch Q2 at which
the bypass switch Q2 is completely turned on). The ON-resistance of
the bypass switch Q2 decreases along with the increase of the gate
voltage, and thus a current flowing through a second light source
22 gradually decrease from a rated current to zero.
[0107] While the duty cycle of the switch control signal S.sub.SC
decreases from 100% to 0%, the drive signal S.sub.D of the driver
19 decreases gradually from the predefined voltage to 0 [V]. The
ON-resistance of the bypass switch Q2 increases along with the
decrease of the gate voltage, and thus the current flowing through
the second light source 22 gradually increase from zero to the
rated current.
[0108] In short, the lighting device of the present embodiment is
configured to gradually change the current flowing through the
second light source 22 in a process of switching the bypass switch
Q2 between an ON-state and an OFF-state, by use of amplification
action of a MOSFET constituting the bypass switch Q2. With this
configuration, the lighting device 1 of the present embodiment can
reduce a stress on the second light source 22 and suppress
flickering of a light source 2 which would otherwise occur during a
process of switching the bypass switch Q2 between the ON-state and
the OFF-state.
[0109] With reference to the time charts of FIGS. 8 and 9,
operations of the lighting device 1 of the present embodiment will
be explained. FIG. 8 shows a case in which the lighting device 1
changes from a main-beam state (a state where a second switch SW2
is turned on) to a low-beam state (a state where the second switch
SW2 is turned off). FIG. 9 shows a case in which the lighting
device 1 changes from the low-beam state (the state where the
second switch SW2 is turned off) to the main-beam state (the state
where the second switch SW2 is turned on).
[0110] An operation of the lighting device 1 switching from the
main-beam state to the low-beam state is explained initially with
reference to FIG. 8.
[0111] When a first switch SW1 is turned on (t=t1), a processor 4
starts performing a constant current control for keeping an output
current of a power converter 3 equal to a target value
(corresponding to a rated current of the light source 2) based on
the above-described manner.
[0112] While the second detection signal S.sub.2 is supplied to the
processor 4 (while a first instruction signal S.sub.I1 is
supplied), a threshold output section 45 sets a first threshold
voltage TH1 as an excess-voltage threshold and sets a third
threshold voltage TH3 as a high-voltage threshold. If no fault
occurs in the light source 2 and the lighting device 1, an output
voltage of the power converter 3 is kept at a first rated
voltage.
[0113] When the second switch SW2 is turned off, the second
detection signal S.sub.2 of the second power supply detector 16
falls to a low-level (t=t2). In response to a falling edge of the
second detection signal S.sub.2, the switch control section 44
starts gradually increasing the duty cycle of the switch control
signal S.sub.SC. The driver 19 gradually increases a voltage level
of the drive signal S.sub.D from 0 [V] to the predefined voltage
according to the switch control signal S.sub.SC (t=t2 to t4). The
ON-resistance of the bypass switch Q2 decreases with the increase
of the voltage level of the drive signal S.sub.D, and as a result
the current flowing through the second light source 22 gradually
decreases from the rated current to zero. Note that the output
voltage of the power converter 3 decreases from time when the
voltage level of the drive signal S.sub.D increases up to a gate
threshold voltage V.sub.G of the bypass switch Q2 (t=t3).
[0114] The processor 4 waits an elapse of a predetermined wait time
period TW from time (t=t2) when the second detection signal S.sub.2
falls to a low-level. Upon determining the elapse of the wait time
period TW, the threshold output section 45 of the processor 4 sets
a second threshold voltage TH2 and a fourth threshold voltage TH4
as the excess-voltage threshold and the high-voltage threshold,
respectively (t=t5). Preferably, the wait time period TW is set to
be comparable to the sum of a time period required for the increase
of the drive signal S.sub.D (t=t2 to t4) and a time required for
the bypass switch Q2 to be completely turned on, and may be set to
around 90 ms. Alternatively, the wait time period TW may be set to
be comparable to the time period required for the increase of the
drive signal SD.
[0115] An operation of the lighting device 1 switching from the
low-beam state to the main-beam state is explained next with
reference to FIG. 9.
[0116] When the first switch SW1 is turned on (t=t1), the processor
4 starts performing the constant current control for keeping the
output current of the power converter 3 equal to the target value
(corresponding to the rated current of the light source 2) based on
the above-described manner.
[0117] While the second detection signal S.sub.2 is not supplied to
the processor 4 (while a second instruction signal S.sub.I2 is
supplied), the threshold output section 45 sets the second
threshold voltage TH2 as the excess-voltage threshold and sets the
fourth threshold voltage TH4 as the high-voltage threshold. If no
fault occurs in the light source 2 and the lighting device 1, the
output voltage of the power converter 3 is kept at a second rated
voltage.
[0118] When the second switch SW2 is turned on, the second
detection signal S.sub.2 of the second power supply detector 16
rises to the high-level (t=t2). In response to a rising edge of the
second detection signal S.sub.2, the switch control section 44
starts gradually decreasing the duty cycle of the switch control
signal S.sub.SC. The driver 19 gradually decreases the voltage
level of the drive signal S.sub.D from the predefined voltage to 0
[V] according to the switch control signal S.sub.SC (t=t2 to t4).
The ON-resistance of the bypass switch Q2 increases with the
decrease of the voltage level of the drive signal SD, and as a
result the current flowing through the second light source 22
gradually increases from zero to the rated current. Note that the
output voltage of the power converter 3 increases from time when
the voltage level of the drive signal S.sub.D decreases and becomes
less than the gate threshold voltage V.sub.G of the bypass switch
Q2 (t=t3).
[0119] Upon detecting the falling edge of the second detection
signal S.sub.2, the threshold output section 45 of the processor 4
sets the first threshold voltage TH1 and the third threshold
voltage TH3 as the excess-voltage threshold and the high-voltage
threshold, respectively (t=t2).
[0120] As described above, in the lighting device 1 of the present
embodiment, the bypass switch Q2 is constituted by a transistor
(specifically, an N-channel enhancement-type MOSFET). The
controller 6 is configured to gradually decrease a current flowing
through the second light source 22 by means of the amplification
action of the transistor in a process of switching the bypass
switch Q2 from the short-circuited state to the open state. The
controller 6 is configured to gradually increase the current
flowing through the second light source 22 by means of the
amplification action of the transistor in a process of switching
the bypass switch Q2 from the open state to the short-circuited
state.
[0121] The lighting device 1 of the present embodiment has the
above described configuration, and accordingly it is possible to
reduce a stress on the light source 2 and suppress flickering of
the light source 2 which would otherwise occur during a process of
switching the bypass switch Q2 between the ON-state and the
OFF-state.
Embodiment 4
[0122] A lighting device 1 according to Embodiment 4 has the same
circuit structure as the lighting device according to Embodiment 1
as shown in FIG. 1. Therefore, detailed explanation and
illustration of the circuit structure of the lighting device 1 of
the present embodiment are again omitted.
[0123] The lighting device 1 of the present embodiment is
characterized by setting a fifth threshold voltage TH5 as an
excess-voltage threshold in a process of switching the bypass
switch Q5 between an ON-state and an OFF-state. Also, the lighting
device 1 of the present embodiment is configured to set a sixth
threshold voltage TH6 as a high-voltage threshold in the process of
switching the bypass switch Q5 between the ON-state and the
OFF-state. The fifth threshold voltage TH5 is smaller than the
first threshold voltage TH1 but larger than the second threshold
voltage TH2. The sixth threshold voltage TH6 is smaller than the
third threshold voltage TH3 but larger than the fourth threshold
voltage TH4.
[0124] Preferably, the processor 4 is configured to decrease the
fifth threshold voltage TH5 of a threshold output section 45 at a
constant rate (-0.2 [V/ms], for example) from the first threshold
voltage TH1 to the second threshold voltage TH2 when detecting a
falling edge of the second detection signal S.sub.2. Also,
preferably, the processor 4 is configured to decrease the sixth
threshold voltage TH6 of the threshold output section 45 at a
constant rate (-0.2 [V/ms], for example) from the third threshold
voltage TH3 to the fourth threshold voltage TH4 when detecting a
falling edge of the second detection signal S.sub.2.
[0125] Preferably, the processor 4 is configured to increase the
fifth threshold voltage TH5 of the threshold output section 45 at a
constant rate (2 [V/ms], for example) from the second threshold
voltage TH2 to the first threshold voltage TH1 when detecting a
rising edge of the second detection signal S.sub.2. Also,
preferably, the processor 4 is configured to increase the sixth
threshold voltage TH6 of the threshold output section 45 at a
constant rate (2 [V/ms], for example) from the fourth threshold
voltage TH4 to the third threshold voltage TH3 when detecting a
rising edge of the second detection signal S.sub.2.
[0126] That is, the lighting device 1 of the present embodiment
uses, during a predetermined time period after switching the bypass
switch Q2 between the ON-state and the OFF-state, a variable fifth
threshold voltage TH5 that varies with an increase in elapsed time,
as the excess-voltage threshold. The processor 4 is configured to
linearly change the fifth threshold voltage TH5 between the first
threshold voltage TH1 and the second threshold voltage TH2 with an
increase in elapsed time after switching the bypass switch Q2
between the ON-state and the OFF-state. Specifically, the processor
4 is configured to decrease the excess-voltage threshold from the
first threshold voltage TH1 to the second threshold voltage TH2 at
a constant rate after switching the bypass switch Q2 from the
OFF-state to the ON-state. Also, the processor 4 is configured to
increase the excess-voltage threshold from the second threshold
voltage TH2 to the first threshold voltage TH1 at a constant rate
after switching the bypass switch Q2 from the ON-state to the
OFF-state.
[0127] Also, the lighting device 1 of the present embodiment uses,
during a predetermined time period from time when after switching
the bypass switch Q2 between the ON-state and the OFF-state, a
variable sixth threshold voltage TH6 that varies with an increase
in elapsed time, as the high-voltage threshold. The processor 4 is
configured to linearly change the sixth threshold voltage TH6
between the third threshold voltage TH3 and the fourth threshold
voltage TH4 with an increase in elapsed time after switching the
bypass switch Q2 between the ON-state and the OFF-state.
Specifically, the processor 4 is configured to decrease the
high-voltage threshold from the third threshold voltage TH3 to the
fourth threshold voltage TH4 at a constant rate after switching the
bypass switch Q2 from the ON-state to the OFF-state. Also, the
processor 4 is configured to increase the high-voltage threshold
from the fourth threshold voltage TH4 to the third threshold
voltage TH3 at a constant rate after switching the bypass switch Q2
from the OFF-state to the ON-state.
[0128] With reference to the time charts of FIGS. 10 and 11,
operations of the lighting device 1 of the present embodiment will
be explained. FIG. 10 shows a case in which the lighting device 1
switches from a main-beam state (a state where a second switch SW2
is on) to a low-beam state (a state where the second switch SW2 is
off). FIG. 11 shows a case in which the lighting device 1 switches
from the low-beam state (the state where the second switch SW2 is
off) to the main-beam state (the state where the second switch SW2
is on).
[0129] An operation of the lighting device 1 switching from the
main-beam state to the low-beam state is explained initially with
reference to FIG. 10.
[0130] When a first switch SW1 is turned on (t=t1), the processor 4
starts performing a constant current control for keeping an output
current of a power converter 3 equal to a target value
(corresponding to a rated current of the light source 2) based on
the above-described manner.
[0131] While the second detection signal S.sub.2 is supplied to the
processor 4 (while a first instruction signal S.sub.I1 is
supplied), a threshold output section 45 sets a first threshold
voltage TH1 as the excess-voltage threshold and sets a third
threshold voltage TH3 as the high-voltage threshold. If no fault
occurs in the light source 2 and the lighting device 1, an output
voltage of the power converter 3 is kept at a first rated
voltage.
[0132] When the second switch SW2 is turned off, the second
detection signal S.sub.2 of the second power supply detector 16
falls to a low-level (t=t2). In response to a falling edge of the
second detection signal S.sub.2, the threshold output section 45
starts decreasing the excess-voltage threshold from the first
threshold voltage TH1 to the second threshold voltage TH2 at the
constant rate (-0.2 [V/ms], for example). In parallel, the
threshold output section 45 starts decreasing the high-voltage
threshold from the third threshold voltage TH3 to the fourth
threshold voltage TH4 at the constant rate (-0.2 [V/ms], for
example). The threshold output section 45 sets the second threshold
voltage TH2 and the fourth threshold voltage TH4 as the
excess-voltage threshold and the high-threshold voltage,
respectively at the time t=t3.
[0133] An operation of the lighting device 1 switching from the
low-beam state to the main-beam state is explained next with
reference to FIG. 11.
[0134] When the first switch SW1 is turned on (t=t1), the processor
4 starts performing the constant current control for keeping the
output current of the power converter 3 equal to the target value
(corresponding to the rated current of the light source 2) based on
the above-described manner.
[0135] While the second detection signal S.sub.2 is not supplied to
the processor 4 (while a second instruction signal S.sub.I2 is
supplied), the threshold output section 45 sets the second
threshold voltage TH2 as the excess-voltage threshold and sets the
fourth threshold voltage TH4 as the high-voltage threshold. If no
fault occurs in the light source 2 and the lighting device 1, the
output voltage of the power converter 3 is kept at a second rated
voltage.
[0136] When the second switch SW2 is turned on, the second
detection signal S.sub.2 of the second power supply detector 16
rises to a high-level (t=t2). In response to a rising edge of the
second detection signal S.sub.2, the threshold output section 45
starts increasing the excess-voltage threshold from the second
threshold voltage TH2 to the first threshold voltage TH1 at the
constant rate (2 [V/ms], for example). In parallel, the threshold
output section 45 starts increasing the high-voltage threshold from
the fourth threshold voltage TH4 to the third threshold voltage TH3
at the constant rate (2 [V/ms], for example). The threshold output
section 45 sets the first threshold voltage TH1 and the third
threshold voltage TH3 as the excess-voltage threshold and the
high-threshold voltage, respectively at the time t=t3.
[0137] As described above, the lighting device 1 of the present
embodiment is configured to set, as the excess-voltage threshold,
the fifth threshold voltage TH5 which is lower than the first
threshold voltage TH1 but higher than the second threshold voltage
TH2, in a process of switching the bypass switch Q2 between the
ON-state and the OFF-state. Further, the lighting device 1 of the
present embodiment is configured to set, as the high-voltage
threshold, the sixth threshold voltage TH6 which is lower than the
third threshold voltage TH3 but higher than the fourth threshold
voltage TH4, in the process of switching the bypass switch Q2
between the ON-state and the OFF-state.
[0138] With this configuration, the lighting device 1 of the
present embodiment can detect an occurrence of a failure such as an
open circuit failure of the light source 2 during a period in which
the lighting device 1 is switched between the main-beam state and
the low-beam state, using the output voltage of the power lighting
device 1 that changes temporarily.
[0139] As described above, in the lighting device 1 of the present
embodiment, the controller 6 (the processor 4; the threshold output
section 45) is configured to, in a process of switching the bypass
switch Q2 between the short-circuited state and the open state,
compare the measured voltage of the voltage meter 13 with the fifth
threshold voltage TH5. The controller 6 is configured to stop the
operation of the power converter 3 by controlling the switching
element Q1 when determining that the measured voltage is equal to
or greater than the fifth threshold voltage TH5. The fifth
threshold voltage TH5 is set to be larger than the second threshold
voltage TH2 but smaller than the first threshold voltage TH.
[0140] The lighting device 1 of the present embodiment has the
above described configuration, and accordingly it is possible to
detect an occurrence of a failure such as an open circuit failure
of the light source 2 even in a period during which the output
voltage of the power converter 3 varies.
Embodiment 5
[0141] A headlight 100 according to Embodiment 5 is explained. As
shown in FIG. 12, the headlight 100 of the present embodiment
includes a lighting device 1 according to any one of Embodiment 1
to 4, a light source 2 (a first light source 21 and a second light
source 22), and a housing 101 in which the light source 2 is
housed. Lamp holders 110 to which LEDs 20 of the first light source
21 and the second light source 22 are attached are provided in the
housing 101. Each lamp holder 110 to which at least one LED 20 of
the first light source 21 is attached is further provided with a
lens 111 and a reflector 112. Each lamp holder 110 to which at
least one LED 20 of the second light source 22 is attached is
further provided with a lens 111.
[0142] As described above, the headlight 100 of the present
embodiment includes the lighting device 1, the light source 2 to be
lit (operated) by the electric power supplied from the lighting
device 1, and the housing 101 that houses the light source 2.
[0143] The headlight 100 of the present embodiment has the above
described configuration, and accordingly it is possible to detect
an occurrence of abnormal output voltage of the power converter 3
while avoiding an occurrence of a failure.
Embodiment 6
[0144] As shown in FIG. 13, a vehicle 200 according to Embodiment 6
includes a vehicle body 201, and two headlights 100 of Embodiment 5
equipped on the vehicle body 201. Lighting devices 1 of the
headlights 100 are electrically connected to a first switch SW1 and
a second switch SW2 which are situated around a driver's sheet in
the vehicle. While only the first switch SW1 is on, a low-beam lamp
(first light sources 21 of the headlights 100) is lit. While both
the first and second switches SW1 and SW2 are on, a main beam lamp
(first light sources 21 and second light sources 22 of the
headlights 100) is lit.
[0145] As described above, the vehicle 200 of the present
embodiment includes one or more headlights 100 and the vehicle body
201 in which the one or more headlights 100 is installed.
[0146] The headlight 100 of the present embodiment has the above
described configuration, and accordingly it is possible to detect
an occurrence of abnormal output voltage of the power converter 3
yet avoid an occurrence of a failure.
[0147] In accordance with the embodiments described above, a
lighting device (1) according to a first aspect is for lighting a
DC light source (2) including a first light source (21) and a
second light source (22). The lighting device (1) includes first to
third output terminals (Y1 to Y3), a power converter (3), a bypass
switch (Q2), and a controller (6). The first output terminal (Y1)
is to be electrically connected to a first end of the first light
source (21). The third output terminal (Y3) is to be electrically
connected to a second end of the first light source (21) and a
first end of the second light source (22). The second output
terminal (Y2) is to be electrically connected to a second end of
the second light source (22). The power converter (3) includes a
DC-DC converter and a pair of output ends (33, 34) electrically
connected respectively to the first and second output terminals
(Y1, Y2). The power converter (3) is configured to supply an output
current from the DC-DC converter through the pair of output ends
(33, 34). The bypass switch (Q2) is electrically connected between
the second and third output terminals (Y2, Y3). The controller (6)
is configured to switch the bypass switch (Q2) between an ON-state
and an OFF-state, and to control the power converter (3) to adjust
the output current of the power converter (3). The controller (6)
includes a voltage meter (13) configured to measure a voltage
corresponding to an output voltage of the power converter (3) to
output a measured voltage. The controller (6) is configured to,
while keeping the bypass switch (Q2) in the OFF-state, compare the
measured voltage of the voltage meter (13) with a predetermined
first threshold voltage (TH1), and stop operation of the power
converter (3) when determining that the measured voltage is equal
to or greater than the first threshold voltage (TH1). The
controller (6) is configured to, while keeping the bypass switch
(Q2) in the ON-state, compare the measured voltage of the voltage
meter (13) with a predetermined second threshold voltage (TH2), and
stop the operation of the power converter (3) when determining that
the measured voltage is equal to or greater than the second
threshold voltage (TH2). The second threshold voltage (TH2) is
smaller than a first rated voltage but larger than a second rated
voltage. The first rated voltage corresponds to a rated value of
the output voltage of the power converter (3) under a condition
where the bypass switch (Q2) is kept in the OFF-state. The second
rated voltage corresponds to a rated value of the output voltage of
the power converter (3) under a condition where the bypass switch
(Q2) is kept in the ON-state. The first threshold voltage (TH1) is
larger than the first rated voltage.
[0148] A lighting device (1) according to a second aspect is
realized in combination with the first aspect, and the controller
(3) is configured to stop the operation of the power converter (3)
when determining that a state where the measured voltage of the
voltage meter (13) is equal to or greater than a predetermined
third threshold voltage (TH3) continues for a predetermined first
upper limit time (TU1) while keeping the bypass switch (Q2) in the
OFF-state. The third threshold voltage (TH3) is larger than the
first rated voltage but smaller than the first threshold voltage
(TH1).
[0149] A lighting device (1) according to a third aspect is
realized in combination with the first or second aspect, and the
controller (6) is configured to stop the operation of the power
converter (3) when determining that a state where the measured
voltage of the voltage meter (13) is equal to or greater than a
predetermined fourth threshold voltage (TH4) continues for a
predetermined second upper limit time (TU2) while keeping the
bypass switch (Q2) in the ON-state. The fourth threshold voltage
(TH4) is larger than the second rated voltage but smaller than the
second threshold voltage (TH2).
[0150] A lighting device (1) according to a fourth aspect is
realized in combination with any one of the first to third aspects,
and the controller (6) is configured to, during a predetermined
wait time period (TW) after switching the bypass switch (Q2) from
the OFF-state to the ON-state or after switching the bypass switch
(Q2) from the ON-state to the OFF-state, compare the measured
voltage of the voltage meter (13) with the first threshold voltage
(TH1), and stop the operation of the power converter (3) when
determining that the measured voltage is equal to or greater than
the first threshold voltage (TH1).
[0151] A lighting device (1) according to a fifth aspect is
realized in combination with any one of the first to fourth
aspects, and the bypass switch (Q2) includes a transistor. The
controller (6) is configured to increase current flowing thorough
the bypass switch (Q2) with an increase in elapsed time in a
process of switching the bypass switch (Q2) from the ON-state to
the OFF-state, and to decrease the current flowing thorough the
bypass switch (Q2) with an increase in elapsed time in a process of
switching the bypass switch (Q2) from the ON-state to the
OFF-state, by means of an amplification action of the bypass switch
(Q2).
[0152] A lighting device (1) according to a sixth aspect is
realized in combination with the first aspect, and the controller
(6) is configured to, during a predetermined time period after
switching the bypass switch (Q2) between the ON-state and the
OFF-state, compare the measured voltage of the voltage meter (13)
with a fifth threshold voltage (TH5), and stop the operation of the
power converter (3) when determining that the measured voltage is
equal to or greater than the fifth threshold voltage (TH5). The
fifth threshold voltage (TH5) is larger than the second threshold
voltage (TH2) but smaller than the first threshold voltage
(TH1).
[0153] A lighting device (1) according to a seventh aspect is
realized in combination with any one of the sixth aspect, and the
controller (6) is configured to linearly change the fifth threshold
voltage (TH5) between the first threshold voltage (TH1) and the
second threshold voltage (TH2) with an increase in elapsed time
after switching the bypass switch (Q2) between the ON-state and the
OFF-state.
[0154] A lighting device (1) according to an eighth aspect is
realized in combination with any one of the first to seventh
aspects, and the first rated voltage is defined by a sum of a rated
voltage of the first light source (21) and a rated voltage of the
second light source (22). The second rated voltage is defined by
the rated voltage of the first light source (21).
[0155] A lighting device (1) according to a ninth aspect is
realized in combination with any one of the first to seventh
aspects, and the first light source (21) is constituted by a series
circuit of LEDs and has a first forward voltage, and the second
light source (22) is constituted by a series circuit of LEDs and
has a second forward voltage. The first rated voltage is defined by
a sum of the first forward voltage and the second forward voltage.
The second rated voltage is defined by the first forward
voltage.
[0156] A lighting device (1) according to a tenth aspect is
realized in combination with the first aspect, and further includes
a signal input terminal (X3) for receiving a first instruction
signal (Su) and a second instruction signal (S.sub.I2). The
controller (6) is configured to, keep the bypass switch (Q2) in the
OFF-state while the signal input terminal (X3) receives the first
instruction signal (Su), and keep the bypass switch (Q2) in the
ON-state while the signal input terminal (X3) receives the second
instruction signal (S.sub.I2).
[0157] A lighting device (1) according to an eleventh aspect is
realized in combination with any one of the first to tenth aspects,
and the DC-DC converter includes a switching element (Q1). The
controller (6) further includes a current meter (14) configured to
measure a current supplied from the power converter (3) to the DC
light source (2), and to output a measured current. The controller
(6) is configured to control a switching operation of the switching
element (Q1) such that the measured current of the current meter
(14) is equal to a predetermined target value. The controller (6)
is configured to, while keeping the bypass switch (Q2) in the
OFF-state, stop the operation of the power converter (3) by turning
off the switching element (Q1) when determining that the measured
voltage is equal to or greater than the first threshold voltage
(TH1), and, while keeping the bypass switch (Q2) in the ON-state,
stop the operation of the power converter (3) by turning off the
switching element (Q1) when determining that the measured voltage
is equal to or greater than the second threshold voltage (TH2).
[0158] A lighting device (1) according to a twelfth aspect is
realized in combination with the eleventh aspect, and the power
converter (3) further includes an inductor (T1) for storing therein
energy in response to supply of electric power from an external DC
power source (B1) while the switching element (Q1) is on, and a
capacitor (C1) to be charged by a regeneration current from the
inductor (T1) while the switching element (Q1) is off. The
controller (6) is configured to generate a primary current
instruction value based on the measured current of the current
meter (14) and the target value. The controller (6) is configured
to turn off the switching element (Q1) when a primary current
flowing through the switching element (Q1) reaches the primary
current instruction value, and turn on the switching element (Q1)
when the regeneration current reaches zero or when a predetermined
suspension time elapses from a time when the switching element (Q1)
is turned on last time.
[0159] A headlight (100) according to a thirteenth aspect includes
the lighting device (1) of any one of the first to twelfth aspects,
a light source (2) to be lit by electric power supplied from the
lighting device (1), and a housing (101) that houses the light
source (2).
[0160] A vehicle (200) according to a fourteenth aspect includes
the headlight (100) of thirteenth aspect, and a vehicle body (201)
in which the headlight (100) is installed.
[0161] While the foregoing has described what are considered to be
the best mode and/or other examples, it is understood that various
modifications may be made therein and that the subject matter
disclosed herein may be implemented in various forms and examples,
and that they may be applied in numerous applications, only some of
which have been described herein. It is intended by the following
claims to claim any and all modifications and variations that fall
within the true scope of the present teachings.
* * * * *